This invention relates to piston cooling systems for internal combustion engines wherein coolant is applied to the rear side of the piston. Such piston cooling systems are known from a number of publications, e.g., DE-OS Nos. 19 05 609 and 20 07 801, as well as DEP No. 2,539,470. In the piston cooling systems described in those publications, the coolant used is the oil which also serves to lubricate the internal combustion engine. According to those publications, the oil is sprayed by nozzles onto the rear of the piston and, to increase the heat transfer, the piston may be provided with ribs or oil-collecting grooves. Thus, the cooling effect of these known piston cooling systems is solely the result of the temperature difference between the piston and the oil.
Increased cooling efficiency for internal combustion engines may be obtained by evaporation cooling arrangements such as described, for example, in DE-OS No. 20 33 960 and DEP No. 3,410,261. Whereas the aforementioned Offenlegungsschrift stresses in particular the construction of a condenser for such a vapor cooling system, DEP No. 3,410,261 describes an evaporation cooling system whereby a coolant is injected into cooling spaces in the cylinder jacket and, respectively, the cylinder head of the internal combustion engine in an amount which is a function of an engine temperature or the load condition of the internal combustion engine by a correspondingly controlled pump. The coolant employed is water with the possible addition of an alcohol suitable for cooling purposes.
Such evaporation cooling devices offer the advantage that their cooling effect results not only from the temperature difference between the coolant and the engine, but also from the additional quantity of heat required for evaporation.
The injection of water into the cylinder space for cooling purposes is also known from DE-OS No. 26 12 378. However, because of the influence of this procedure on the combustion process, it can be utilized only in certain cases. Furthermore, the water injected is used up during operation of the engine.